Flyback to replace bug zapper HV transformer

Discussion in 'Power Electronics' started by Dwayne Oxford, Jul 13, 2016.

  1. Dwayne Oxford

    Thread Starter New Member

    Mar 22, 2015
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    Original has 4 wires, flyback has 3. Not sure how to wire it up. Need ignorance relief.
     
  2. Roderick Young

    Member

    Feb 22, 2015
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    I don't really know how those zappers are hooked up, but if the transformer has 4 wires, that suggests that the primary is isolated from the secondary. You could check that with an ohmmeter, seeing if there are two pairs of wires that appear to not be connected with each other. If the flyback has 3 wires, that suggests that there's just one winding with taps. That would sacrifice electrical isolation, and could be a potential safety issue.
     
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  3. Lestraveled

    Well-Known Member

    May 19, 2014
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    How about a photo or two. Show old HV transformer and flyback.
     
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  4. Benengineer

    Member

    Feb 6, 2016
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    Do you have any picture?
     
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  5. Dwayne Oxford

    Thread Starter New Member

    Mar 22, 2015
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    Will post pics soon's I get another out of old monitor.. 1st 2 flybacks I salvaged were bad.
     
  6. ian field

    Distinguished Member

    Oct 27, 2012
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    You don't need a CRT flyback transformer to incinerate flying insects.

    The chopper transformer from a cheap flyback SMPSU can be made to generate a healthy arc between the previously primary pins.

    My DIY pocket xenon strobe was developed for 4.8V Ni-Cds and prototyped with a 5V SMPSU. The first attempt had no regulation and arced impressively.

    The problem you might be having with CRT flybacks is; The scan yokes form part of the inductive components that is tuned by a capacitor - you may have to find the suitable frequency by trial and error - a diode-split LOPT may not like the frequency you end up with.
     
  7. Dwayne Oxford

    Thread Starter New Member

    Mar 22, 2015
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    Here they be! S2010001.JPG S2010002.JPG S2010003.JPG S2010004.JPG
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Have you considered an ignition coil alternative?
    Max.
     
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  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Is this a mains powered zapper?
    Use auto HV coil for L1.
    [​IMG]


    Max.
     
  10. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    What you have there is a TV Lopt, which is tuned to 15khz, and will need an hv supply of around 150v dc.

    You're better using an ht coil from a car.
     
  11. ian field

    Distinguished Member

    Oct 27, 2012
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    Not if you use the heater winding as the primary.

    TV coils usually have a heater winding - monitor coils usually don't.

    The best scan/EHT transformer to use is; the really old type that had external tripler. The modern diode-split type can be awkward to drive - particularly; you have to get the flyback polarity right. In normal use; they're 5th harmonic tuned and won't produce as much EHT unless you add tuning capacitance. Not to mention; the scan yoke is a critical inductive component in tuning the whole system.

    Its far easier (and more compact) to use the flyback chopper transformer from the PSU in a scrap set top box or DVD player.
     
  12. tcmtech

    Well-Known Member

    Nov 4, 2013
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    To be honest I would recommend just buying a smaller neon sign transformer to replace your old one being that's what many bug zappers use anyway.

    Also given the long run times and relatively harsh working environment that a bug zapper is used in one of those will stand up to that sort of environment and application far better than any old TV flyback unit will.

    If you do a bit of online searching you can easily pick up 4 - 6KV NST's for $20 - $30.
     
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  13. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I was thinking of setting up a bug zapper, I have an ignition coil and maybe experiment with the circuit in post #9, advantage is it is low voltage supply.
    Max.
     
  14. ian field

    Distinguished Member

    Oct 27, 2012
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    Having acquired some 8uF 2.5kV capacitors - I'm seriously tempted to try a capacitor discharge bug zapper.

    2.5kV should be enough to explode the average fly.
     
  15. Dwayne Oxford

    Thread Starter New Member

    Mar 22, 2015
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    It's out of computer monitor. I thought it ran off
    Yes.
    It's out of a computer monitor. I thought 120 V AC would power it. I'm electronics ignorant though.
     
  16. ian field

    Distinguished Member

    Oct 27, 2012
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    If you apply 120V 60Hz to the primary of a scan/EHT transformer - it'll let the magic smoke out along with other entertaining forms of excitement.

    Monitor EHT transformers operate from at least 15kHz to 64kHz (maybe more). An oscillator/inverter circuit is one approach, the original primary winding will require at least 60V drive, so the design won't be trivial. You also have to get the phasing the right way round on a diode-split transformer.

    Monitor transformers don't usually have a 6.3V winding for the CRT heater, but there may be other windings that can be driven by a lower voltage. Sometimes the supply for the vertical output is derived from a winding on the transformer - that may work from an easier voltage to handle.

    You can get a very hot arc from a 4.8V Ni-Cd pack and a backwards chopper transformer from a scrap DVD player/set top box etc - its much easier to design around and a lot more compact.
     
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  17. Dwayne Oxford

    Thread Starter New Member

    Mar 22, 2015
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    So, bottom line, this ain't gonna work. Sounds like time to explore the neon transformer. Do appreciate the response.
     
  18. tcmtech

    Well-Known Member

    Nov 4, 2013
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    There are ways to make the more complicated circuits work but why bother? All you want to do is kill bugs as reliably as possible for as little work and money as possible.
     
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  19. Dwayne Oxford

    Thread Starter New Member

    Mar 22, 2015
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  20. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Should work fine assuming 2500 volts is high enough for your zapper. Many of the larger better-built ones can run up in the 3000 - 4000 range.

    I say buy it and give it a test! I would think that 2500 volts should be enough to strike an arc through a bug. :D
     
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